How Natural Processes Operate at Coastal Geographic Environment
Natural Processes are actions or events that have natural causes, which result in natural events. The three main coastal environment processes that operate at Muriwai are Coastal Erosion, Coastal Transportation and Coastal Deposition.
The elements that interact to produce natural processes are wind, waves and tides. Each phenomenon at Muriwai's coastal geographic environment has been produced by interaction.
Coastal Erosion is a process at Muriwai that gradually wears away the rock particles of the earth's surface, transporting them to another location. There are many types of processes that cause erosion at Muriwai such as wave erosion, wind erosion and wave refraction.
Thousands of years ago when sea levels dropped over years at the Southern end of Muriwai, the sedimentary rock and sandstone was exposed to the air. Rock from volcanic activity mixed with the sedimentary rock; this is called Breccia -- a mixture of all rock. An example of this is at Maori Bay.
Coastal Erosion operates at different rates and different times. Limestone rock is eroded slower than sedimentary rock. The cliff at Muriwai made of sedimentary rock was eroded back to expose 'Fisherman's Rock' - the shore platform which, made of limestone -- tended to erode back slower than the cliff.
The types of wave erosion that caused this are -
Hydraulic Action, when waves hit the cliff, air is forced into cracks, and then as the wave retreats this air expands explosively. Over time the cracks enlarge, weakening the base of the cliff causing erosion.
Attrition is the breakdown of rock particles when they hit Otakamiro point and each other causing the base of the headland to erode.
Chemical Erosion/Corrosion occurs due to the content of limestone in the rockface of Otakamiro point. The seawater combined with the limestone produces a weak chemical solution, which erodes the base of the cliff and produces a pitted effect.
Chemical Weathering is when water weakens the structure of the rock and Mechanical Weathering is where water seeps into the rock face causing fragments of rock to break off.
These types of erosion have caused the formation of several phenomena at Muriwai.
Motutara Island (stack) was produced by the formation of two caves on either side of the headland -- forming an arch and the roof slowly eroding away due to vertical erosion.
Fisherman's Rock was produced by cliff retreat when undercutting stones are thrust at the cliff by wave action.
The blowhole was formed by vertical, hydraulic and mechanical erosion causing the cracks and fissures to enlarge over time to produce this hole.
Types of wave erosion operating on the headland have produced the cave.
Wave Refraction is an important process as it influences wave erosion on Otakamiro headland and on the beach at Muriwai (refer to Diagram 1). Wave Transportation (Longshore Drift) varies spatially due to wave refraction. It is the...